Evaporator fan delay circuit

ABSTRACT

A refrigerator control circuit is provided for delaying the starting of the air circulating freezer fan until after the free moisture on the evaporator coils has frozen upon the completion of a defrost cycle. A single throw-double pole defrost limiter thermostat controlled by a bimetal snap acting disc having one set of contacts closing to the freezer fan and its remaining set of contacts closing to the defrost heater, thereby preventing the freezer fan from being energized until the evaporator has returned to below freezing after the completion of the defrost cycle.

'United States Patent Canter Dec. 2, 1975 1 1 EVAPORATOR FAN DELAY CIRCUIT Primary Examiner-William E. Wayner 75 l t A. C t E l d, Oh 1 nven or James an H ng ewoo l0 Attorney, Agent, or Firm-Edward P. Barthel [73] Assignee: General Motors Corporation,

Detroit, Mich. ABSTRACT [22] Filed: Nov. 27, 1974 App]. No.: 527,692

A refrigerator control circuit is provided for delaying the starting of the air circulating freezer fan until after the free moisture on the evaporator coils has frozen upon the completion of a defrost cycle. A single throw-double pole defrost limiter thermostat controlled by a bimetal snap acting disc having one set of contacts closing to the freezer fan and its remaining set of contacts closing to the defrost heater, thereby preventing the freezer fan from being energized until the evaporator has returned to below freezing after the completion of the defrost cycle.

3 Claims, 1 Drawing Figure U.S. Patent Dec. 2, 1975 a I w I w W i w. Ll w. 7 4. a z. m z C E u a i 54% m w 5 v3 1 Q. [a n EVAPORATOR FAN DELAY CIRCUIT This invention relates to refrigerating apparatus and more particularly to a fan control circuit for use in defrosting the cooling coil of a refrigerator.

The control circuits used in prior art refrigerators for controlling the operation of the refrigeration system have not been entirely successful in preventing the addition of heat or free moisture to the food compartment by virtue of the freezer fan circulating relatively warm moist air adjacent the evaporator throughout the cabinet immediately after the defrosting operation.

It is an object of this invention to provide a simple and inexpensive, yet reliable improved refrigerator control system which will prevent the operation of the air circulating freezer fan until after the free moisture on the evaporator coils has been frozen.

It is another object of this invention to provide an improved evaporator fan delay circuit for a domestic frost free refrigerator with a defrost evaporator heater wherein a single throw-double pole defrost limiter thermostat controlled by thermal element in the form of a snap acting disc with the thermostat having a pair of leads from one side of an electrical power source such that the first lead of said pair is connected to one set of contacts closing to the evaporator fan motor and the other lead connected to the other set of contacts closing to the defrost heater while a single lead from the thermostat contacts is connected to the other side of the power source obviating an electrical path through the compressor motor windings with the resultant premature energizing of the evaporator fan before the evaporator is lowered to a below freezing temperature. In the Drawing:

The drawing shows somewhat schematically a refrigerator embodying the invention.

Referring now to the drawing wherein a preferred arrangement has been shown, reference numeral generally designates a refrigerator cabinet having a food storage compartment 12 which is adapted to be refrigerated by means of an evaporator 14 which for purposes of illustration is located in an air duct adjacent the food storage compartment 12. The evaporator 14 forms a part of a conventional refrigeration system including a compressor 18 which withdraws vaporized refrigerant from the evaporator 14 and discharges compressed refrigerant into the condenser 20 from whence the liquid refrigerant flows to the evaporator 14 through a capillary tube type of restrictor 22. A freezer fan 24 is used to circulate air from the food compartment over the evaporator coils which serves to cool the air before being returned and distributed to the freezer compartment of the refrigerator in a customary manner as shown by US. Pat. 3,203,199 issued to D. 0. Stewart and assigned to the same assignee as the present invention.

The evaporator 14 must be defrosted from time to time such as once every 8 hours and for that purpose there is provided an electric heater 26 which is arranged in thermal exchange relationship with the evaporator 14 and which serves to supply heat for defrosting the evaporator in a manner to be described more fully hereinafter. Power for operating the refrigerator and its controls is supplied through the power supply lines L, and L2.

A defrost timer 28 including a timer motor 29 controls the movable contact arm 30 of a double-throw switch which serves to selectively energize either the defrost heater 26 via switch contact 31 and line 32 or the circuit for the compressor-motor 18 via switch contact 33, line 34, cold control 36, lines 37 and 38 to motor protector 40, and thence via line 41 to motor relay 42 at its terminal 43. The defrost timer, which in the preferred form is of the type shown and described in US. Patent application Ser. No. 497,337 serves to move the switch from its full line position to its dotted line position once every 8 hours. The movable contact switch 30 has been shown in its run position in contact with contact 33 wherein it supplies current to the line 34 and the temperature or cold control thermostat 36. The thermostat 36 responds to refrigeration requirements and serves to close the circuit to the line 37 whenever refrigeration is required. The thermostat 36 is preferably located in the above freezing compartment or in the return air duct and opens the circuit to the freezer fan 24 and the compressor 18 at 5 F. and recloses at +5 F. When the movable contact arm of cold control thermostat 36 is in its closed position, both the freezer fan 24 and the compressor 18 will operate.

In the disclosed embodiment the timer synchronous motor 29 moves the movable contact arm 30 to its dotted line position at contact 31 to deenergize the freezer fan 24 and the compressor 18 and energize the defrost heater 26 once every 8 hours. The heater 26 is connected to L of the power source by line 45 and blade contact 30 contacting fixed contact 31 which in turn is connected via lines 32 and 46 to one side of the defrost heater 26 while the other side of the heater 26 is connected by line 48 to fixed contact 49 of a double polesingle throw defrost limiter thermostat generally indicated at 50. The thermostat 50 has its first fixed contact 49 which may be closed by a first switch blade movable contact 52 connected by wire 53 to wire 54 which is in turn connected to the other side of the line indicated by L of the power source.

The defrost limiter thermostat 50 also includes a second set of contacts namely, second fixed contact 56 connected via wire to the other side of the evaporator or freezer fan motor 24 while its movable contact blade 57 is connected via wire 58 and wire 54 to the line L side of the power source. The defrost limiter thermostat thermal element in the form of a bimetal disk 60 is designed to open both sets of contacts 51, 52 and 56, 57, which are normally closed at the beginning of a defrost cycle, upon the rise of temperature adjacent the evaporator to about 55 F. or at the end of the defrosting operation, thereby simultaneously opening the circuit to both the defrost heater 26 and the evaporator freezer fan 24. The bimetal disc has a snap acting dished portion which causes it to move with snap-like motion from one concave configuration to an opposite convex one and back upon predetermined changes in temperature. Thus, the freezer fan 24 is delayed from turning on until after the free moisture on the evaporator coils has been frozen by the cooling process initiated by the return of the defrost timer movable contact arm 30 being returned to contact its fixed contact 33.

The defrost heater 26 and the freezer fan motor 24 will remain deenergized until the bimetal disk 60 snaps back at a temperature of about 30 F. wherein both movable contact blades 52 and 67 close simultaneously to their fixed contacts 49 and 56 respectively, completing an electrical path from the freezer fan motor 24 to the other side of the power source at L It will be appreciated that by virtue of applicants arrangement a circuit is created which eliminates the possibility of any sneak electrical flow path being set up if the freezer fan 24 were wired from L, through mullion dryer 61, wire 62, defrost heater 26, the freezer fan 24, wire 38, protector 40, wire 41, windings 64 of relay 42, wire 65 through the windings 66 of the compressor motor via line 66 and thence to the L side of the power source by line 67.

The condenser fan motor 70 is energized when the cold control thermostat 36 movable contact 35 closes since wire 37 is connected via wire 38, motor protector 40, wire 41 and wire 72 to one side of the line L,, while the wire 74 connects the other side of the line L to the fan motor 70. A conventional lamp switch 76 has a movable contact 78 which closes to energize the refrigerator lamp 80. The timer motor 29 is connected by line 86 and line 45 to the L side of the power source while line 88 connects the other side of the motor 29 to the L side of the power source.

While in the preferred form the defrost timer 28 turns off the compressor 18 and blower or freezer fan motor 24 and, at the same time, energizes the defrost heater 26 and the drain heater 82 three times in every 24 hours, it will be appreciated that other timing intervals could be adopted such as having two defrost cycles every 24 hours.

While the embodiment of the present invention herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

I claim:

1. In combination, a refrigerator cabinet having an insulated above-freezing food storage compartment and a freezer food storage compartment therein, a source of electrical power, an evaporator positioned in the freezer compartment, means including a freezer fan for circulating air through the compartments in thermal exchange relationship with said evaporator, a compressor for supplying liquid refrigerant to said evaporator, temperature responsive cold control switch means connecting said compressor to said power source, defrost timer means for periodically defrosting said evaporator including an electric defrost heater arranged in thermal exchange relationship with said evaporator, said timer means including a single pole double throw switch for selectively energizing either said compressor or said electric defrost heater, a single throw double pole defrost limiter thermostatic switch having a first set of contacts connecting one side of said power source in series circuit with said defrost heater to the other side of said power source, said defrost limiter switch having a second set of contacts connecting one side of the power source in series circuit with said freezer fan, said cold control switch means, and said defrost timer means to the other side of the power source during a cooling cycle; whereby upon the said defrost limiter thermostatic switch sensing a predetermined evaporator temperature above freezing, said defrost limiter switch first and second set of contacts simultaneously opening deenergizing said defrost heater and disconnecting said freezer fan from said one side of said power source, respectively; and said defrost limiter switch first and second set of contacts simultaneously closing at a predetermined temperature below freezing, whereby said freezer fan is energized by virtue of the said closed second set of contacts completing a circuit from said one side of said power source through said fan, said cold control switch means and said defrost timer switch means to the other side of said power source while said defrost heater is removed from the one side of said power source by said defrost limiter switch until the next defrost cycle initiated by said defrost timer switch means.

2. In combination, a refrigerator cabinet having an insulated above-freezin g food storage compartment and a freezer food storage compartment therein, a source of electrical power, an evaporator positioned in the freezer compartment, means including a freezer fan for circulating air through the compartments in thermal exchange relationship with said evaporator, a compressor for supplying liquid refrigerant to said evaporator, a temperature responsive thermostatic cold control switch connecting said compressor to said power source, a defrost timer for periodically defrosting said evaporator including an electric defrost heater arranged in thermal exchange relationship with said evaporator, said defrost timer including a single pole double throw switch for selectively energizing either said compressor or said electric defrost heater, a single throw double pole defrost limiter thermostatic switch having a snap-acting thermoresponsive disc element actuating a first set of contacts connecting one side of the power source in series circuit with said defrost heater to the other side of said power source, said defrost limiter thermostatic disc actuating a second set of contacts connecting one side of said power source in series circuit with said freezer fan, said cold control switch, and said defrost timer to the other side of the power source during a cooling cycle; whereby upon the said defrost limiter thermostatic disc sensing an evaporator temperature above about 50 F. said defrost limiter switch first and second set of contacts simultaneously opening deenergizing said defrost heater and disconnecting said freezer fan from said one side of said power source, respectively, and said defrost limiter switch first and second sets of contacts simultaneously closing at a below freezingtemperature, whereby said freezer fan is energized by virtue of the said closed second set of contacts completing a circuit from one side of said power source through said fan, said cold control switch and said defrost timer switch to the other side of said power source, while said defrost heater is removed from one side of the power source until the next defrost cycle of said defrost timer switch.

3. In a refrigerator evaporator defrost control system for operating a compressor motor, freezer fan motor, defrost heater and defrost timer motor; a circuit for controlling the operation of the refrigerator including first and second supply conductors for energizing the circuit, a single pole double throw defrost timer switch having a movable contact connected to said first supply conductor, one fixed contact of said timer switch connected to one electrical path through a cold control thermostatic switch and said compressor motor to said second supply conductor, said timer one fixed contact connected to a second electrical path through said cold control switch and the freezer fan motor to one fixed contact of a single throw double pole defrost limiter thermostatic switch having a snap-acting bimetal disc actuator, said defrost timer motor connected between said first and second supply conductors so as to be energized to run continuously, said timer switch movable contact being moved by said timer motor at predetermined time intervals to its other fixed contact connecting said first supply conductor through said defrost timer interval said timer motor moving said timer switch movable contact to its one fixed contact, whereby said compressor motor is energized to resume the cooling cycle of the refrigerator while said defrost limiter disc holds its first and second movable contacts in open circuit position until said evaporator reaches a predetermined temperature below freezing to thereby prevent said freezer fan from being energized until said evaporator has been cooled to said predetermined below freezing temperature. 

1. In combination, a refrigerator cabinet having an insulated above-freezing food storage compartment and a freezer food storage compartment therein, a source of electrical power, an evaporator positioned in the freezer compartment, means including a freezer fan for circulating air through the compartments in thermal exchange relationship with said evaporator, a compressor for supplying liquid refrigerant to said evaporator, temperature responsive cold control switch means connecting said compressor to said power source, defrost timer means for periodically defrosting said evaporator including an electric defrost heater arranged in thermal exchange relationship with said evaporator, said timer means including a single pole double throw switch for selectively energizing either said compressor or said electric defrost heater, a single throw double pole defrost limiter thermostatic switch having a first set of contacts connecting one side of said power source in series circuit with said defrost heater to the other side of said power source, said defrost limiter switch having a second set of contacts connecting one side of the power source in series circuit with said freezer fan, said cold control switch means, and said defrost timer means to the other side of the power source during a cooling cycle; whereby upon the said defrost limiter thermostatic switch sensing a predetermined evaporator temperature above freezing, said defrost limiter switch first and second set of contacts simultaneously opening deenergizing said defrost heater and disconnecting said freezer fan from said one side of said power source, respectively; and said defrost limiter switch first and second set of contacts simultaneously closing at a predetermined temperature below freezing, whereby said freezer fan is energized by virtue of the said closed second set of contacts completing a circuit from said one side of said power source through said fan, said cold control switch means and said defrost timer switch means to the other side of said power source while said defrost heater is removed from the one side of said power source by said defrost limiter switch until the next defrost cycle initiated by said defrost timer switch means.
 2. In combination, a refrigerator cabinet having an insulated above-freezing food storage compartmEnt and a freezer food storage compartment therein, a source of electrical power, an evaporator positioned in the freezer compartment, means including a freezer fan for circulating air through the compartments in thermal exchange relationship with said evaporator, a compressor for supplying liquid refrigerant to said evaporator, a temperature responsive thermostatic cold control switch connecting said compressor to said power source, a defrost timer for periodically defrosting said evaporator including an electric defrost heater arranged in thermal exchange relationship with said evaporator, said defrost timer including a single pole double throw switch for selectively energizing either said compressor or said electric defrost heater, a single throw double pole defrost limiter thermostatic switch having a snap-acting thermoresponsive disc element actuating a first set of contacts connecting one side of the power source in series circuit with said defrost heater to the other side of said power source, said defrost limiter thermostatic disc actuating a second set of contacts connecting one side of said power source in series circuit with said freezer fan, said cold control switch, and said defrost timer to the other side of the power source during a cooling cycle; whereby upon the said defrost limiter thermostatic disc sensing an evaporator temperature above about 50* F. said defrost limiter switch first and second set of contacts simultaneously opening deenergizing said defrost heater and disconnecting said freezer fan from said one side of said power source, respectively, and said defrost limiter switch first and second sets of contacts simultaneously closing at a below freezing temperature, whereby said freezer fan is energized by virtue of the said closed second set of contacts completing a circuit from one side of said power source through said fan, said cold control switch and said defrost timer switch to the other side of said power source, while said defrost heater is removed from one side of the power source until the next defrost cycle of said defrost timer switch.
 3. In a refrigerator evaporator defrost control system for operating a compressor motor, freezer fan motor, defrost heater and defrost timer motor; a circuit for controlling the operation of the refrigerator including first and second supply conductors for energizing the circuit, a single pole double throw defrost timer switch having a movable contact connected to said first supply conductor, one fixed contact of said timer switch connected to one electrical path through a cold control thermostatic switch and said compressor motor to said second supply conductor, said timer one fixed contact connected to a second electrical path through said cold control switch and the freezer fan motor to one fixed contact of a single throw double pole defrost limiter thermostatic switch having a snap-acting bimetal disc actuator, said defrost timer motor connected between said first and second supply conductors so as to be energized to run continuously, said timer switch movable contact being moved by said timer motor at predetermined time intervals to its other fixed contact connecting said first supply conductor through said defrost heater to the other fixed contact of said defrost limiter switch, said defrost limiter switch having a single conductor connecting both its first and second movable contacts to said second supply conductor, after the energization of said defrost heater by said timer upon said defrost limiter disc sensing the evaporator temperature above about 50* F. simultaneously opening both said defrost limiter first and second movable contacts deenergizing said defrost heater and opening the circuit between said freezer fan and said second supply conductor, and upon the completion of said predetermined timer interval said timer motor moving said timer switch movable contact to its one fixed contact, whereby said compressor motor is energized to resume the cooling cycle of the refrigErator while said defrost limiter disc holds its first and second movable contacts in open circuit position until said evaporator reaches a predetermined temperature below freezing to thereby prevent said freezer fan from being energized until said evaporator has been cooled to said predetermined below freezing temperature. 